To cope with more stringent regulations against vapor emission of fuel gases in the automotive field or other fields in recent years, high barrier properties against fuels have been investigated. Moreover, in order to reduce the weight of vehicles (such as an automobile) for improving fuel efficiency, the use of resins for fuel-related devices or peripheral devices thereof increases every year for reducing the weight of these devices. In response to the point, the demand for the fuel-barrier property of resins has increased. A fluorine-series resin, a poly(butylene naphthalate) (hereinafter, sometimes referred to as PBN), and others are known as a resin having a high barrier property against fuels. For example, Japanese Patent Application Laid-Open No. 96564/1995 (JP-7-96564A (Claims)) discloses a fuel transport tube which has an innermost layer comprising a resin selected from the group consisting of a fluorine resin and a polyamide-series resin, an intermediate layer comprising a poly(alkylene naphthalate) resin (e.g., a poly(butylene naphthalate)), an outer layer composed of a thermoplastic resin or a thermoplastic elastomer, and an adhesive layer formed between the innermost layer and the intermediate layer. Japanese Patent Application Laid-Open No. 23930/1994 (JP-6-23930A (Claims)) discloses a multilayer polymer hose or pipe which has at least a blocking layer comprising a polyester (such as a poly(butylene terephthalate) or a PBN) and is a coextrusion product.
However, there is a trend to restrict the use of halides including the fluorine-series resin for environmental reasons. In addition, it is difficult to bond or adhere the fluorine-series resin to another member, and the fluorine-series resin is unsuitable for a multilayer product. On the other hand, for the polyester such as the PBN, it is necessary to improve hydrolysis resistance in the case of using the polyester for a monolayer product. Alternatively, it is necessary to form a multilayer structure containing a layer formed of the polyester and a layer formed of a soft material. Thus, there was reported a product which was obtained by treating a surface of a polyester resin layer with plasma or sputter to convert the surface to a surface having an adhesive property and coating the polyester resin layer with a nylon or the like.
Japanese Patent Application Laid-Open No. 272630/2006 (JP-2006-272630A (Claims)) relates to a fuel hose having improved low-temperature characteristics, softness, and hydrolysis resistance and discloses a three-layer (or three-ply) fuel hose comprising a tubular inner layer, a layer having a low permeability to a fuel and being adjacent to and surrounding an outer peripheral surface of the inner layer, an outer layer being adjacent to and surrounding an outer peripheral surface of the low-permeability layer. In the fuel hose, the inner layer comprises a polyester resin softened by alloying or copolymerizing with use of an elastomer component, the low-permeability layer comprises at least one polyester-series resin selected from the group consisting of a poly(butylene naphthalate) and a poly(butylene terephthalate), and the outer layer comprises a blend polymer of a styrene-isobutylene block copolymer and a polyester elastomer whose copolymer component is at least one selected from the group consisting of a poly(tetramethylene glycol) and a dimer acid. Japanese Patent Application Laid-Open No. 261078/2007-(JP-2007-261078A (Claims)) relates to a fuel hose having improved low-temperature resistance, softness, hydrolysis resistance, weather resistance, and ozone resistance and discloses a three-layer (or three-ply) fuel hose comprising the same tubular inner layer and low-permeability layer (or layer having a low permeability to a fuel component) as mentioned above and an outer layer being adjacent to and surrounding an outer peripheral surface of the low-permeability layer and comprising a blend polymer of a poly(butylene terephthalate) and at least one member selected from the group consisting of a polymer fine particle having a core-shell structure, an ethylene-acrylic rubber (AEM), and a styrene-isobutylene copolymer. However, the elastomer component is required to have improved weather resistance to ozone or a light beam such as xenon. Moreover, the polystyrene-series elastomer such as the styrene-isobutylene block copolymer has an insufficient compatibility (or miscibility) with a poly(butylene terephthalate) or a polyester-series elastomer, which is a problem for the combination use. Therefore, the use of a compatibilizer (e.g. an ethylene-glycidyl methacrylate copolymer; EGMA) for overcoming the problem has been also reported.